472 General Notes. [May 
ied by the pradacite of Lang, and its contact zone. By com- 
parison of the composition of an unaltered slate with that of a 
hornfels produced by its alteration, 5 is seen that in this process 
water and carbon dioxide were driven off, and the ferric iron in 
_ the former was reduced to the BRON state in the latter. The 
brown mica of the hornfels contains 3.40 per cent. of titanic 
oxide. 
tes.—Although the interesting bodies known as light- 
statutes have been the subjects of numerous papers during 
the past century, it must be confessed that our knowledge in 
regard to them is not very extensive. The United States National 
Museum having recently become possessed of several fine speci- 
mens of the tubular varieties formed by lightning striking in loose 
sand, Mr. G. P. Merrill* has been enabled to s study these micro- 
scopically, and thus to add something to our previous knowledge 
of them. In all the cases examined the walls of the tubes con- 
sisted of glass, in which there were no traces of crystallization. 
Analyses of the glass and of the sand in which the fulgurites 
` are found and by the fusion of which they were produced, show 
that in every case the former contains more silica than the latter. 
The author argues that “had the lightning shown no selective 
—i.¢., to be a very poor conductor of electricity. It would then 
in consequence of this resistance become heated even to the 
point of fusion, while the better conductors would escape with 
little injury. The resulting glass would in this case have a 
higher percentage of = ces the surrounding sand. The 
sides County, Ill., yendi n Clarke: 
Loss on ignition SiO, Fe.0, .Al,O; CaO MgO K,O Na,O 
a Piai 0.33 9I 1.66 6.69 038 612 073 097 
Sand 1.01 84.83 9.88 £56 -013 L13 1.50 
The paper concludes with a very full bibliography of the subject. 
Mineralogical News.—A variety of the rare mineral carpho- 
coy ated is described by Lacroix? from the triassic cies of 
Macon {Saône-et-Loire}. It occurs as micaceous coatings 
Messe 2 United States National Museum, 1886, p. 83. 
2 Comptes us, ciii., 1886, p. 1037. 
